1. Field of the Invention
The present invention relates to a dust core, and more particulary to a coil-embedded dust core, which may be used in inductors having a unitary structure with a magnetic core and in other electronic components. The present invention also relates to a method for manufacturing the coil-embedded dust core.
2. Description of Related Art
In recent years, electric and electronic equipment has become more compact, and dust cores that are compact (low in height) yet able to accommodate large current have come to be in demand.
Materials used for dust cores are ferrite powder and ferromagnetic metal powder, but ferromagnetic metal powder has larger saturation magnetic flux density than ferrite powder and its DC bias characteristics may be maintained even in a strong magnetic field. Consequently, in making a dust core that can accommodate large current, using ferromagnetic metal powder as a material for dust core has become mainstream.
In addition, in order to further the effort to make the core more compact (lower in height), a coil body in which a coil and compacted magnetic powder form a unitary structure has been proposed. In the present specification, an inductor having such a structure may be called a xe2x80x9ccoil-embedded dust core.xe2x80x9d
A manufacturing method for a surface-mount type inductor having a structure of a coil-embedded dust core has been proposed in the past. For example, an exterior electrode is connected to an insulation-coated lead wire, and these are enclosed in magnetic power, which is then formed into a magnetic body. In this case, connection parts are inside the magnetic body, which makes them prone to failures while molding. In the present specification, a xe2x80x9cconnection partxe2x80x9d refers to a part where components are electrically connected to each other, and a part where a component is connected to an external electrode is called a xe2x80x9cterminal section.xe2x80x9d
Conventionally, a method of compression-molding flat powder and a coil using a binder is known. For example, the conventional method includes the steps of making a composite material using a Fexe2x80x94Alxe2x80x94Si metal alloy powder with an aspect ratio of approximately 20 and a silicone resin as an insulating material, and compression-molding the composite material together with a coil. However, no consideration has been given to connection parts between the coil and terminal sections, and joint failures are likely to occur due to the fact that joining is difficult since it takes place between the magnetic body section and an electrode at the interface with the core.
Furthermore, a method of manufacturing an inductor using ferrite as a magnetic material is known. Here again, part of the terminal that forms a connection part with the coil is inside the core, which makes it prone to failures in the connection parts during the process to form a unitary structure.
Also, in one conventional method, an inductor is manufactured by compression-molding a coil and a terminal section while having them vertically interposed in a green body. Failures are likely to occur in the connection parts in this case as well.
As stated above, a coil-embedded dust core has a structure in which large inductance can be obtained in spite of its small size. However, as electric and electronic equipment becomes rapidly more compact, the demand for improved quality of coil-embedded dust core is growing. Specifically, there are demands to prevent joint failures between a coil and terminal sections; to prevent insulation failures of a coil and terminal sections with respect to magnetic powder; to make components even more compact; and to have larger inductance.
The coil-embedded dust core or the inductor proposed in the conventional art can be improved in terms of quality. Namely, the coil-embedded dust core or the inductor in the conventional art has a coil and terminal sections embedded within magnetic powder, which makes it prone to joint failures between the coil and the terminal sections or insulation failures of the coil and the terminal sections with respect to the magnetic powder. When a joint failure or an insulation failure occurs, it is difficult to determine the cause of the failure and in many cases takes a long time, since the coil and the terminal sections form connection parts inside the magnetic powder.
Furthermore, the conventional inductor entails a high possibility for a joint failure to occur in connection parts between a coil and terminal sections after molding, due to the fact that a dust core is made using a coil that already has connection parts formed with terminal sections. When a joint failure occurs in a connection part, determining the cause is difficult and time-consuming.
In view of the above, it is an object of the present invention to provide a coil-embedded dust core that is not prone to joint failures between a coil and terminal sections or to insulation failures of the coil and terminal section with respect to magnetic powder; that is more compact; and that can provide larger inductance; and to provide a method for manufacturing such a coil-embedded dust core.
The inventors of the present invention have found that by using a coil that is formed from a flat conduction wire, a coil-embedded dust core can be made even more compact while offering larger inductance.
In accordance with one embodiment of the present invention, a coil-embedded dust core comprises a green body consisting of ferromagnetic metal particles coated with an insulating material, and a coil embedded inside the green body wherein the coil is formed from a wound flat conductor coated with an insulation. In one aspect of the present invention, the green body may be a compacted body of magnetic powder including at least ferromagnetic metal particles coated with an insulating material.
In the present invention, the coil may be formed from a rectangular wire wound in a coil. Also, parts of the coil may function as terminal sections. In this case, it would be effective to form the terminal sections to be wider than other parts of the coil. In order to form the wider sections, lead-out end sections of the rectangular wire may be subject to a flattening process. In addition, in the present invention, front and back surfaces of the end sections of the coil may be exposed outside the green body.
In the present invention, the green body may have a structure with front and back surfaces that oppose each other across a predetermined space and side surfaces formed around the front and back surfaces, and each of the end sections of the coil may extend outside the green body along one of the side surfaces.
The present invention further provides a coil-embedded dust core, comprising a green body in a rectangular solid shape having front and back surfaces that oppose each other across a predetermined space and side surfaces formed around the front and back surfaces. There is also a coil having a winding section and end sections pulled out from the winding section, wherein at least the winding section of the coil is placed inside the green body, and end section housing chambers each of which opens to one of the side surfaces of the green body and houses one of the end sections of the coil exposed from the green body.
The end section housing chambers of the coil-embedded dust core according to the present invention may be formed in corner sections of the green body.
Furthermore, the present invention provides a coil-embedded dust core comprising magnetic powder consisting of ferromagnetic metal particles coated with an insulating material, and a coil embedded inside the magnetic powder, wherein the core includes a dust core section molded from the magnetic powder, and the coil is connected to terminal sections (i.e., the coil and the terminal sections form connection parts) outside the dust core section. In order to form the connection parts between the coil and the terminal sections outside the dust core section molded from the magnetic powder, the terminal sections may be extended from side surfaces to a bottom surface of the dust core section. These terminal sections function as surface-mount terminals.
The present invention also provides a coil-embedded dust core comprising a magnetic powder consisting of ferromagnetic metal particles coated with an insulating material, and a coil embedded inside the magnetic powder, wherein the coil is not connected to terminal sections (i.e., the coil and the terminal sections do not form connection parts).
The present invention provides a method for manufacturing a coil-embedded dust core in which a coil is embedded within a green body, the method comprising a preformed body obtaining step, in which a coil wound around with a flat, insulation-coated conductor is placed in a raw material powder whose elements are ferromagnetic metal powder and an insulating material that forms the green body. There is also a compression formation step of compacting the raw material powder.
In the preformed body obtaining step, it is effective to place parts of the coil that make up the terminal sections outside the raw material powder, and to perform, after the compression formation step, a heat treatment step of heat treatmenting the insulating material, a rust-proofing step of forming a rust-proof film on the surface of the terminal sections of the coil, and a sandblasting step of sandblasting the surface of the terminal sections.
Other objects, features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.